TOO MUCH OF A GOOD THING
(1 Hour)
Addresses NGSS
Level of Difficulty: 4
Grade Range: 3-5
OVERVIEW
In this activity, students will explore the potential dangers of overusing certain antibacterial products such
as soaps, shampoos and other wash products.
Topic: Microbiology, Natural Selection and Adaptations
Real-World Science Topics
• An exploration of biological and evolutionary processes that lead to resistant bacteria known as “superbugs”
• An exploration of how genetic changes can create beneficial characteristics (known as adaptations) which
allow organisms to better survive in changing conditions
Objective
After completing this activity, students should be able to explain how certain chemicals found in antibacterial
agents can lead to strains of resistant “super” bacteria and why this is dangerous.
NGSS Three-Dimensions
Science and Engineering
Practices
1
Disciplinary
Core Ideas
Planning and Carrying Out
Investigations
• Make observations and/or
measurements to produce
data to serve as the basis for
evidence for an explanation
of a phenomenon or test a
design solution.
3-LS3.B: Variation of Traits
• Different organisms vary in
how they look and function
because they have different
inherited information.
• The environment also affects
the traits that an organism
develops.
Analyzing and
Interpreting Data
• Represent data in tables
and/or various graphical displays (bar graphs, pitographs,
and/or pie charts) to reveal
patterns that indicate
relationships.
• Analyze and interpret data
to make sense of phenomena,
using logical reasoning, mathematics, and/or computation.
3-LS4.B: Natural Selection
• Sometimes the differences
in characteristics between
individuals of the same
species provide advantages
in surviving, finding mates,
and reproducing.
3-LS4.C: Adaptation
• For any particular environment,
some kinds of organisms
survive well, some survive
less well, and some cannot
survive at all.
Crosscutting
Concepts
Patterns
• Similarities and differences in
patterns can be used to sort,
classify, communicate and
analyze simple rates of change
for natural phenomena and
designed products.
• Patterns of change can be
used to make predictions.
Cause and Effect
• Cause and effect relationships
are routinely identified,
tested, and used to explain
change.
Stability and Change
• Change is measured in terms
of differences over time and
may occur at different rates.
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TOO MUCH OF A GOOD THING
Planning and Carrying Out
Investigations
• Collect data to produce
data to serve as the basis for
evidence to answer scientific
questions or test design
solutions under a range
of conditions.
Analyzing and
Interpreting Data
• Construct, analyze, and/or
interpret graphical displays of
data and/or large data sets to
identify linear and nonlinear
relationships.
• Analyze and interpret data
to provide evidence for
phenomena.
Constructing Explanations
and Designing Solutions
• Apply scientific ideas,
principles, and/or evidence
to construct, revise and/or
use an explanation for realworld phenomena, examples,
or events.
2
MS-LS4.B: Natural Selection
• Natural selection leads to
the predominance of certain
traits in a population, and the
suppression of others.
MS-LS4.C: Adaptation
• Adaptation by natural selection acting over generations
is one important process by
which species change over
time in response to changes
in environmental conditions.
Traits that support successful
survival and reproduction in
the new environment become
more common; those that
do not become less common.
Thus, the distribution of traits
in a population changes.
Patterns
• Patterns can be used to
identify cause and effect
relationships.
• Graphs, charts, and images
can be used to identify
patterns in data.
Cause and Effect
• Cause and effect relationships
may be used to predict
phenomena in natural or
designed systems.
Stability and Change
• Explanations of stability and
change in natural or designed
systems can be constructed
by examining the changes
over time and forces at
different scales, including
the atomic scale.
• Stability might be disturbed
either by sudden events
or gradual changes that
accumulate over time.
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TOO MUCH OF A GOOD THING
Background Information
Is bacteria good or bad?
Bacteria can be both good and bad. Some bacteria cause diseases but many are completely harmless and
in some cases very beneficial. For example, in humans some strains of bacteria help us with digestion while
others help in the production of vitamins.
Can bacteria easily mutate and change to better survive the changing condition of their
environment?
Because bacteria reproduce rather quickly and have a relatively small genome (set of DNA), they tend to
mutate rather easily. Because of this, colonies of bacteria can quickly develop adaptations. These adaptations allow the bacteria to survive better in the changing conditions of their environments.
Is the statement, “what doesn’t kill you makes you stronger” true for bacteria?
In a sense, this statement is true. As bacteria are exposed to a different environment or chemical for extended periods of time, the weaker and less resistant bacteria tend to die off. However, the stronger bacteria
tend to mutate and adapt to the new environment or chemical exposure. These mutant bacteria are said to
be resistant. Over many generations, these resistant bacteria multiply. If these bacteria are disease-causing,
they can become a huge heath risk because they are harder to treat and/or kill. These type of bacteria are
often referred to as “superbugs.”
Are all antibacterial products created equal?
No. Only some antibacterial products contain the chemical triclosan or it close relative triclocarban. These
two chemicals have proven to cause resistant bacteria in laboratory test. Unlike the chemical triclosan
which lingers on the skin and gradually kills bacteria over an extended period of time, alcohol-based hand
sanitizers work quickly at killing bacteria and then evaporate. Bacteria tend to mutate more efficiently
if exposed to a chemical or adverse condition over a prolonged period of time. This is not the case with
alcohol-based sanitizer; they do their job and then dissipate.
How can chemicals such as triclosan found in antibacterial products lead to resistance
in bacteria?
Because chemicals such as triclosan leave a residue on the skin after application, bacteria are exposed to
low levels of the chemical over a long period of time. This sets up an ideal situation for bacteria to mutate
and adapt. The weaker bacteria die off leaving the genetically supierior bacteria. These stronger bacteria
can mutate and become genetically resistant to chemical exposure.
Do all scientists agree that triclosan can be a potential danger?
No. Some scientists argue that these laboratory findings cannot be recreated in real-world situation and
should therefore not be considered dangerous.
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TOO MUCH OF A GOOD THING
Materials Needed for Student Activity
Materials Needed for Demonstration:
• Antibacterial hand soap containing triclosan (see label on soap)
Materials Needed to Prepare for the Student Activity:
• Pure grape or cranberry juice (unsweetened in case of spills)
• Baking Soda
• Cookie sheets (with sides)
• Bacteria cutout templates (included in activity)
• Scissors or paper cutter
• Permanent marker
Materials Needed for Each Team of 2-3 Students:
• 4 labeled snack-size zip bags filled with paper bacteria (see “Teacher Preparation” section for details)
• Cotton swabs
• Small plastic cups
Teacher Preparation
Before students arrive you will need to prepare the following materials.
Preparing the paper bacteria cutouts:
• A note before beginning. Keep in mind the end goal it so make 5 piles of cut pieces using the templates
included in this activity. Make sure to keep 5 distinct piles (beneficial in water, beneficial in baking soda,
disease-causing in water, disease-causing in baking soda, and disease-causing with mutation) because
there is no way to tell the difference between the cutouts soaked in baking soda verses water pieces
once you have cut them out.
• Prepare a baking soda solution by mixing about 3 to 4 tablespoons of baking soda with about 1 liter
of warm water and mixing well.
• Pour the baking soda solution into a cookie sheet (or other flat container that can hold fluid). Enough
to cover a few sheets of stacked paper.
• Pour about the same amount of filtered (or distilled) water into a second cookie sheet/container.
• Next you will need to print the bacteria cutouts using the templates provided. Note that there are
100 cutouts per pages. Calculate how many bacteria cutouts you will need to print using the following
formulas:
Number of teams X 33 = “beneficial bacteria cutouts” to be soaked in water (see example for help)
Number of teams X 30 = “beneficial bacteria cutouts” to be soaked in baking soda
Number of teams X 14 = “disease-causing bacteria” cutouts to be soaked in water
Number of teams X 15 = “disease-causing bacteria” cutouts to be soaked in baking soda
Number of teams X 11 =
4
“disease-causing bacteria with mutation” cutouts to be soaked in baking
soda (none are soaked in water)
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TOO MUCH OF A GOOD THING
(For example: If there were 5 teams in my class, I would need 165 beneficial bacteria cutouts
(5 x 33 = 165). This means I would need to print 2 pages of them and soak 1 full pages plus 65
from the 2nd page.)
• Print the correct number of templates for each type of bacteria.
• Place the templates in the appropriate cookie sheet and soak for 30 seconds or so.
• Allow sheets to air dry for several hours. For quicker drying, place sheets in microwave on high heat
until dry.
• Cut out the bacteria pieces. Use a paper cutter to significantly speed up this process.
Remember to keep the cut pieces in 5 distinguishable piles.
• Prepare 4 zip bags (per team) with bacteria cut outs as follows:
• Using a permanent marker, label the bags:
“Initial bacteria collection at 7:00 AM”
“Bacterial collection 12:00 PM”
“Bacterial collection 5:00 PM”
“Bacterial collection 10:00 PM”
• Fill the bags according to the chart below.
Beneficial in
water
Beneficial in
baking soda
7:00 AM
11
9
2
4
0
12:00 PM
9
8
3
2
1
5:00 PM
7
8
4
4
3
10:00 PM
6
5
5
5
7
Bag
Disease-causing Disease-causing Disease-causing
in water
in baking soda
with mutation
• Prepare cups of cranberry or grape juice:
Label each cup “Antibacterial Soap with Triclosan” (1 cup per team)
Fill each cup about 1/3 of the way full with undiluted juice.
Place a cotton swab in each cup
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STEPS FOR
1.
TOO MUCH OF A GOOD THING
Warm-up Activity: Ask students to write a sentence in their science journals or a blank sheet of paper
using one of the following three sentence stems.
Bacteria are good because….
Bacteria are bad because…
Bacteria are good and bad because…
Write the three sentence stems on the board so students can reference those as they write their
sentence. Handout the student page for this activity as they write.
2.
After students have had some time to complete their sentence, ask for a few volunteers to share. Use
this discussion time to inform students about the diversity of bacteria and the fact that bacteria can
be good as well as bad. Students need to understand that some bacteria can cause diseases such as
Tuberculosis, food poisoning, pneumonia, and strep throat. It is equally important that students understand that most bacteria are not harmful at all, and in fact, are extremely beneficial to humans. Some
beneficial bacteria help us digest our food, produce needed vitamins, and these good bacteria crowd
out bad bacteria.
3.
Students should be encouraged to fill in the Fact vs. Myth Box on their handout as discussions take
place throughout the activity.
4.
Show students a bottle of pre-purchased antibacterial soap (containing triclosan) and explain that it is
a special kind of soap with a chemical. This chemical stays on your skin even after you have washed and
dried your hands and slowly kills some kinds of bacteria.
5.
Pose the question, “are antibacterial soaps such as this [show the soap] a good thing or a bad thing?”
Allow students to argue and discuss this question before moving on to the next portion of the activity.
At this point, do not give students an explanation to the question. Allow them to explore the answer
as they complete the activity.
6.
Read the following paragraphs to the students.
“Today you will take on the role of a research scientist. The question posed to you is, “what effects
do antibacterial soaps containing triclosan have on bacteria?” [Write this question on the board for
students to reference.]
You will be given samples of bacteria collected from a test subject over the period of a day. The subject
is using antibacterial soap containing triclosan at various times during the day. It is your job as a scientist
to study, record and analyze the data from the collections. You must answer the question posed to you
as a scientist and make a recommendation to others about using or not using soaps such as this one
[show the soap].
Because only highly trained microbiologists can work with real disease-causing bacteria, we are going
to use other materials to simulate what microbiologists have discovered in labs.”
7.
Divide students into teams of 3 or 4. Give each team a cup labeled “antibacterial soap with triclosan”
and a baggie labeled “beginning bacteria collection”. Make sure students know that the solution in the
cup simulates antibacterial soap. Point out that there are different kinds of bacteria in the bag and that
they are labeled for distinction.
8.
Ask students to open the bag, count the bacteria and record the data on their student handout.
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STEPS FOR
9.
TOO MUCH OF A GOOD THING
Have students spread the bacteria (pieces of paper) out on the table. Using a cotton swab, rub a bit of
the antibacterial agent (grape juice solution) from the cup on each one of the bacteria. If the bacteria
turns a green color, the chemical kills it. Students should record their data in the column labeled “Use of
soap with triclosan 7:10AM.”
10. Ask students to discard the material from the first test. Give them a second bag labeled “bacteria
collection 12:00PM.” Repeat the steps outlined above until all of the bacteria samples are tested.
11. Ask students to graph their data on their student handout using a line graph.
The teacher should graph the data on the board as students complete the graph on their student sheet.
12. Give students time to graph and analyze their data. Based on the data analysis, students should work
together to develop a recommendation about using antibacterial soaps on a frequent basis. They must
be able to justify their recommendation using data.
13. Have a couple of groups give their recommendations and justifications to class.
14. Wrap-up: Discuss the following points with students.
• Bacteria are extremely small and cannot be counted or collected as simply as they did in this
simulation. Microbiologist must use very specialized methods to count and collect these bacteria.
• Some laboratory experiments using antibacterial agents that contain triclosan have shown results
similar to the results they saw in their simulation. This has led some scientist to warn consumers that
over using antibacterial agents with chemicals such as triclosan can lead to disease causing superbacteria that are resistant to chemicals such as antibacterial agents and antibiotics.
• There is ongoing research on this topic and some scientists argue that such findings in the laboratory
do not necessarily mean that it happens in real-world settings.
• Antibiotics have proven to have similar affects on bacteria as well.
• There is concern among doctors and scientists that resistant super-bacteria could cause a deadly
outbreak sometime in the future.
• For more information on this topic, see the 2007 Scientific American article “Strange But True:
Antibacterial Products May Do More Harm Than Good” by Coco Ballantyne.
Extension Activity
Challenge students to find and document products containing triclosan or triclocarban in their home. Give
students a chance to share how many and what products they found. You should encourage them to look
at cleaning products, soaps, shampoos, lotions, hand sanitizers, toothpastes, laundry detergents, or anything
else labeled “antibacterial.”
Sources
http://www.tufts.edu/med/apua/about_issue/agents.shtml
http://www.fda.gov/forconsumers/consumerupdates/ucm205999.htm
http://www.beyondpesticides.org/antibacterial/triclosan.php
Ballantyne, Coco. “Strange but True: Antibacterial Products May Do More Harm Than Good.”
Scientific American, 07 June 2007. Web. 20 Apr. 2013.
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TOO MUCH OF A GOOD THING
STUDENT HANDOUT
Name:
Date:
Bacteria: Truth vs. Myth Box
As you learn facts and/or myths about bacteria, record them in the box below.
Facts
Myths
What is the name of the antibacterial chemical agent found in some soaps that you will be studying today?
________________________
Data
Use of
Use of
Initial
Use of
Use of
Bacteria
Bacteria
Bacteria
soap with
soap with
bacteria soap with
soap with
collection
collection
collection
triclosan
triclosan
triclosan
collection triclosan
Time of Action
7:00 AM
7:15 AM
12:00 PM
12:10 PM
5:00 PM
5:10 PM
10:00 PM
Beneficial
Bacteria
Disease-causing
Bacteria
Mutant
Disease-causing
Bacteria
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10:10 PM
TOO MUCH OF A GOOD THING
STUDENT HANDOUT
Data Analysis
Key
Good bacteria
Bad bacteria
Bad bacteria
with mutation
22
20
18
Number of Bacteria
16
14
12
10
8
6
4
2
10:10 PM
10:00 PM
5:10 PM
5:00 PM
12:10 PM
12:00 PM
7:10 AM
7:00 AM
0
Time
Recommendation: Based on your data analysis, write a recommendation to your friends about using
antibacterial products such as soaps, shampoos, and other wash products that contain chemicals such
as triclosan. You must include the following terms: resistant bacteria, mutation, antibacterial, and triclosan.
_________________________________________________________________________________________
_________________________________________________________________________________________
_________________________________________________________________________________________
_________________________________________________________________________________________
_________________________________________________________________________________________
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TOO MUCH OF A GOOD THING
TEACHER HANDOUT
Bacteria: Truth vs. Myth Box
As you learn facts and/or myths about bacteria, record them in the box below.
Facts
Myths
Examples:
• Bacteria can be good and bad
• Some bacteria help in digestion
• Some bacteria help produce important
vitamins
• Antibacterial agents with chemicals, such as
triclosan, slowly kill bacteria
• Bacteria’s genetic material tends to change and
mutate to help it survive changing conditions
• Laboratory studies show that long-term
exposure to chemicals, similar to triclosan,
can cause resistant strains of bacteria to form
Examples:
• All bacteria are harmful and cause disease
• All antibacterial agents contain chemicals
such as triclosan.
• All bacteria mutate and are able to survive
harsh environments.
• All scientists agree that triclosan can cause
resistant bacteria that are harder to killed
with antibiotics and antibacterial agents.
What is the name of the antibacterial chemical agent found in some soaps that you will be studying today?
Triclosan
Data
Use of
Use of
Initial
Use of
Use of
Bacteria
Bacteria
Bacteria
soap with
soap with
soap with
bacteria soap with
collection
collection
collection
triclosan
triclosan
triclosan
collection triclosan
Time of Action
7:00 AM
7:15 AM
Beneficial
Bacteria
20
11
Disease-causing
Bacteria
6
Mutant
Disease-causing
Bacteria
0
10
12:00 PM
12:10 PM
5:00 PM
5:10 PM
10:00 PM
10:10 PM
17
9
15
7
11
6
2
5
3
8
4
10
5
0
1
1
3
3
7
7
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TOO MUCH OF A GOOD THING
TEACHER HANDOUT
Data Analysis
Key
Good bacteria
Bad bacteria
Bad bacteria
with mutation
22
20
18
Number of Bacteria
16
14
12
10
8
6
4
2
10:10 PM
10:00 PM
5:10 PM
5:00 PM
12:10 PM
12:00 PM
7:10 AM
7:00 AM
0
Time
Recommendation: Based on your data analysis, write a recommendation to your friends about using
antibacterial products such as soaps, shampoos, and other wash products that contain chemicals such
as triclosan. You must include the following terms: resistant bacteria, mutation, antibacterial, and triclosan.
Answers will vary.
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TOO MUCH OF A GOOD THING
BENEFICIAL BACTERIA TEMPLATE - 100 COUNT
12
Beneficial
Beneficial
Beneficial
Beneficial
Beneficial
Beneficial
Beneficial
Beneficial
Beneficial
Beneficial
Beneficial
Beneficial
Beneficial
Beneficial
Beneficial
Beneficial
Beneficial
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Beneficial
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Beneficial
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Beneficial
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Beneficial
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Beneficial
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Beneficial
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Beneficial
Beneficial
Beneficial
Beneficial
Beneficial
Beneficial
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DISEASE-CAUSING BACTERIA TEMPLATE - 100 COUNT
13
Disease-causing
Disease-causing
Disease-causing
Disease-causing
Disease-causing
Disease-causing
Disease-causing
Disease-causing
Disease-causing
Disease-causing
Disease-causing
Disease-causing
Disease-causing
Disease-causing
Disease-causing
Disease-causing
Disease-causing
Disease-causing
Disease-causing
Disease-causing
Disease-causing
Disease-causing
Disease-causing
Disease-causing
Disease-causing
Disease-causing
Disease-causing
Disease-causing
Disease-causing
Disease-causing
Disease-causing
Disease-causing
Disease-causing
Disease-causing
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Disease-causing
Disease-causing
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Disease-causing
Disease-causing
Disease-causing
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Disease-causing
Disease-causing
Disease-causing
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DISEASE-CAUSING WITH MUTATION BACTERIA TEMPLATE - 100 COUNT
14
Disease-causing
with Mutation
Disease-causing
with Mutation
Disease-causing
with Mutation
Disease-causing
with Mutation
Disease-causing
with Mutation
Disease-causing
with Mutation
Disease-causing
with Mutation
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with Mutation
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with Mutation
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